1. Field of the Invention
This invention relates to a mobile phone antenna and, particularly, to a mobile phone antenna that the bandwidth can be broadened without raising the position of an antenna element and that can prevent displacement in resonance frequency in a folding type mobile phone where the position of a board ground is shifted when folded.
2. Description of the Related Art
Mobile phones and PHS (personal handyphone system) phones are provided with a telescoping whip antenna and a built-in planar antenna so as to facilitate the receiving and transmitting with the base station. The planar antenna used is generally inverted F antenna that has a miniaturized size, a simplified structure and broad bandwidth characteristics.
FIG. 1 is a perspective view showing a conventional inverted F antenna for mobile phone. The inverted F antenna 100 for mobile phone is provided with a ground plane 101 as a printed circuit board which is installed in the housing of mobile phone, and the ground plane 101 is composed of interconnection pattern and metal conductors. Above the ground plane 101, there is provided a planar antenna radiation element 102 of metal plate. Further, a ground connector 103 and a feed point 104 are provided to connect the ground plane 101 with the antenna radiation element 102.
However, in the convention inverted F antenna, it is necessary to raise, by a certain height, the antenna element 102 from the ground plane 101 since the bandwidth narrows according as the antenna element 102 comes closer to the ground plane 101. Furthermore, since the inverted F antenna is apt to be affected by the ground of printed circuit board (board ground), there occurs a displacement in resonance frequency when the position of board ground varies as the upper and lower housings are opened or closed that are equipped with a folding type mobile phone.